transactions: fix hg recover with fncache backups The transaction backupfiles logic was broken for 'hg recover'. The file format is XXX\0XXX\0YYY\0YYY\0 but the parser did a couple things wrong. 1) It went one step beyond the final \0 and tried to read past the end of the array. 2) array[i:i+1] returns a single item, instead of two items as intended. Added a test to catch it, which turns out to be the first actual 'hg recover' test.

  $ hg init

  $ echo 123 > a
  $ hg add a
  $ hg commit -m "first" a

  $ mkdir sub
  $ echo 321 > sub/b
  $ hg add sub/b
  $ hg commit -m "second" sub/b

  $ cat sub/b
  321

  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cat sub/b 2>/dev/null || echo "sub/b not present"
  sub/b not present

  $ test -d sub || echo "sub not present"
  sub not present